Abstract Congestive heart failure (CHF) is a major health problem in the USA that affects about 5.7 million Americans. The incidence of CHF is steadily increasing as the general population ages. The national cost of CHF is estimated around $30.7 billion each year. Although the mortality rate and the economic impact of CHF are high, the detailed molecular mechanisms underlying its progression remain unresolved. Understanding the fundamental processes that drive cardiac functional and structural deterioration is essential for developing novel therapies to more fundamentally affect disease progression. The stress-induced cardiac hypertrophy is an essential step in the pathogenesis of many forms of CHF, and its suppression is a viable target for therapeutic intervention. Stromal interaction molecule1 and 2 (STIM1, STIM2) and its molecular partners Orai proteins (Orai1, Orai2, and Orai3) constitute the store-operated Ca2+ channel (SOCC) and are surfacing as new potential therapeutic targets against pathological heart hypertrophy. Results from our published work provide strong evidence, that STIM1 forms Ca2+ microdomains that control cardiac growth via signaling that alters the cytoskeleton and pro-hypertrophic gene program. However, Orai(s) contribution to the progression of the failing heart is unknown. We have generated cardiac-specific Orai1 and Orai3 knockout mice and find that Orai1 associated with Ca2+\calmodulin pathway, while Orai3 is associated prevalently with the PI3K/AKT pathway. We hypothesize that Orai1- and Orai3-dependent Ca2+ signaling are distinct but together orchestrate the cardiac hypertrophic response. Dysregulation of cardiac Ca2+ and oxidative stress appear to be symbiotic in CHF, a corollary to this hypothesis is that selective inhibition of Orai proteins will reduce oxidative stress of the diseased heart. This project seeks to manipulate Orai channels to decrease and reverse cardiac functional deterioration in CHF. We plan to test our central hypothesis by pursuing the following specific aims: Aim 1: Test the hypothesis that Orai1- and Orai3-configurations have different spatial localizations, activation mechanisms, and downstream gene programs. Aim 2: Test the hypothesis that selective genetic ablation of Orai1 or Orai3 attenuates cardiac hypertrophy and delays the transition to CHF. Aim 3: Test the hypothesis that inactivation of hypertrophic signaling cascades by Orai gene ablation during established cardiac hypertrophy prevents the transition to CHF and improves oxidative stress. This work will lead to elucidation of the molecular mechanism by which Orai(s) regulates heart function; the identification of Orai as a novel mediator of CHF; potentially identify new strategies aimed at reversing or delay the oxidative stress and functional derangements seen in CHF.